The overall goal os this project is to ascertain the murine in vivo mechanisms involved in beta-endorphin and met-enkephalin-mediated immunomodulation. The cumulative evidence linking opioid peptides to the immune system suffers from three principal drawbacks: 1) in vitro systems ignore the normal architecture of the immune system, 2) the use of physical stressors to induce opioid analgesia also release of glucocorticoids which modulate immune function, and 3) in vivo studies utilizing one-time bolus injections of peptides also result in the release of glcocorticoids. The next logical step in the study of opioid peptide-mediated modulation is to show modulation in vivo, and in the absence of corticosteroids. The approach taken in this proposal is the use of a mini-osmotic pump delivery system for the continuous administration of peptides over 3-7 day periods. This system reduces animal stress and subsequent release of corticosteroids. The initial goal is to determine levels of infused opioid peptides required to alter immune function, as measured buy plaque-forming cell and cytotoxic T-cell assays following immunization, natural killer cell activation, and spleen cell proliferation following mitogen stimulation. In addition to measurements of serum opioid peptide levels (to insure the maintenance of physiologic concentrations), all experimental animals will be monitored for serum glucocorticoids as a determinant of stress. The second goal is to determine phenotypic alterations of spleen cell populations using flow cytometry. The third and major objective is to determine the mechanism(s) involved in opioidmediated immunomodulation including assessments of: 1) antigen presentation and production of IL-1 by spleen adherent cells, 2) T helper cell activity and production of IL-2, and 3) suppressor cell activity. In order to determine if opiate receptors are involved, animals will receive with the peptide an opiate receptor antagonist, such as naloxone. Completion of this project will give further insight into the role of stress-related neuropeptides in altering immune function and host resistance to malignancy and infection, and will lead to a more precise understanding of the in vivo interactions between the neuroendocrine and immune systems. Furthermore, these studies could provide additional information on the possible side effects resulting from the therapeutic uses of opioid peptides for the treatment of pain and cancer.